CNN  — 

Poll of the week: A new Monmouth University poll finds former Vice President Joe Biden with a 53% to 41% lead over President Donald Trump.

The average live interview poll conducted over the last month has Biden ahead by a similar 11-point margin.

What’s the point: Usually, this is the point where someone like myself says we have four months to go until the election and polls are a snapshot in time. Both of those statements are true, but they obscure an important fact.

Polls taken around Independence Day in an election year are actually pretty highly correlated with the November results in incumbent contests. That means Trump is in a lot of trouble.

Take a look at the 13 incumbent elections dating all the way back to 1940. Usually going all the way back in time will lead you to find a lot of volatile campaigns, as more modern ones tend to be more steady.

Yet, since 1940, the final result differs from the polls at this point by an average of just 7 points. The median difference is only about 4.5 points.

View Trump and Biden head-to-head polling

These should be quite worrisome for Trump given he’s already down double-digits, and there’s no guarantee any polling miss would benefit him.

Indeed, we can translate past polling to give us odds about the current election. At least 8-in-10 to 9-in-10 times based solely on the horserace polling, Biden would be expected to take more votes in the fall.

More troublesome for Trump: no one in an incumbent presidential election has been polling above 50% at this point like Biden and gone on to lose.

In other words, Trump already needs something quite unusual to occur in order to come back in this race.

Many of the previously hopeful examples for Trump are no longer ones that should make Trump happy.

Republican Wendell Willkie significantly cut an over 20-point deficit in early 1940 to be within about 10 points of Democrat Franklin Roosevelt in July 1940. Willkie would lose by 10 points.

Democrat Jimmy Carter had jumped out to a mid-single digit advantage over non-elected incumbent Republican Gerald Ford in early July 1976, after being down in the winter. Carter would win by 2 points in the fall.

Republican Ronald Reagan blew past Carter to an 11-point lead by early July in 1980 despite trailing by double-digits a few months earlier. Reagan emerged victorious by 10 points in the fall.

Even Republican George H.W. Bush’s lead over Democrat Bill Clinton had turned into basically a tie by this point, after Clinton was down nearly 40 points in some of the earliest polling of the race. By July 10, Clinton was ahead in some polling before going on to win by a little less than 6 points in the fall.

View 2020 presidential election polling

There have been only two races since 1940 in which the difference between the polls now and the eventual result was greater than the margin by which Trump is down now.

Democrat Lyndon Johnson’s 56-point blowout edge over Republican Barry Goldwater translated into a 23-point blowout in the fall. Johnson’s advantage, however, defied the bounds of political gravity, as he still was likely benefiting from a polling bump after succeeding the assassinated John Kennedy.

The only really good example for Trump is Democrat Harry Truman in 1948. He was down by a little over 10 points to Republican Thomas Dewey. Truman would win by a little less than 5 points. Unlike Biden, however, Dewey was under 50%.

Now, the past isn’t necessarily prologue. There is time for volatility. The polls will probably bounce around during the convention period. (Part of the reason the first 10 days of July are a good snapshot is that it is usually after the primary season but before the conventions.) Trump could close the gap and could very well win.

But make no mistake: An incumbent trailing by double-digits in early July with an opponent over 50% is a heavy underdog for reelection.